NEW DEVELOPMENTS IN PION NUCLEAR-PHYSICS BELOW AND ABOVE THE DELTA-REGION

A brief review and discussion is made of a few topics concerning the pion nucleus interaction at low energies and above the delta region. A many body description of the pion nuclear optical potential at low energies is presented by means of which one obtains a fair reproduction of the data of pionic atoms, including the former 'anomalous atoms', and of the scattering data at low energies in all different reaction channels: elastic, quasielastic and absorption. A connection between the second order optical potential and the ''absorption contribution' to the double charge exchange process is made and results are shown for this latter reaction. Of particular interest is the application made of pionic atom data to extract information on neutron distributions in nuclei. At high energies we show some small but systematic discrepancies between theory and experiment which call for some explanation. On the other hand the former and large discrepancies between theory and experiment in single and double charge exchange find a natural explanation by means of the core polarization which renormalizes the isovector piN scattering amplitude.